The present invention pertains generally to microwave generators and more particularly to microwave generators for converting the energy of an intense relativistic beam (REB) into a high-powered microwave emission.
The present invention utilizes the Smith-Purcell effect, see S. J. Smith and E. M. Purcell, Phys. Rev. 92, 1069 (1953) and G. Toraldo di Francia, Nuovo Cimento 16, 61 (1960). The Smith-Purcell effect is related to Cerenkov radiation, see I. M. Frank and I. Tamm, Dokl. Akad. Nauk. 14, 109 (1937) and J. V. Jelley, Cerenkov Radiation and its Applications, (Pergamon Press, NY, 1958).
Early efforts in this field have demonstrated the feasibility of generating high frequency radiation by passing a beam between the standing wave pattern formed by a grating and a reflector, see U.S. Pat. Nos. 2,634,372 and 2,866,917 issued to W. W. Salisbury. A row of hemispheres have been embedded in a plane as a Smith-Purcell radiator, again in the reflection mode rather than the transmission, see J. A. Bradshaw, Proc. Symp. on Millimeter Waves (Polytechnic Press, NY 1960), p. 223. Also, experiments have been performed that produced infrared radiation using reflection gratings and non-relativistic beams, see K. Ishiguro and T. Tako, Optica Acta 8, 25 (1961).
However, none of the above teaches the coupling of a magnetized relativistic electron beam (REB) excited transmission to a resonator as in the present invention to form an efficient generator or amplifier of frequency stable microwaves. Further, none of the above teaches the use of the radiation at 90.degree. to achieve superior frequency stability.
The present invention satisfies the need for a high-power, monochromatic microwave source for laboratory experiments with microwave-impulse air breakdown at 35 GHz and below. This power requirement suggests the use of a pulse-power REB excited microwave tube. However, for most pulse-power REBs, the beam energy continuously varies during the pulse, and the microwave output frequency would not be monochromatic, but swept, if it were strongly dependent on the beam energy. The present invention circumvents this annoyance.